Submarine pipelines, for example for transporting petroleum or gas from offshore production fields may be made from steel pipe sections which are welded together on a special vessel, and the pipeline may be placed in position at the bottom of the sea as the pipe sections are being welded together. In order to secure that the pipeline remains in the desired position at the bottom at the sea, the pipe sections may be given a negative buoyancy by providing the outer peripheral surface of each pipe section with a layer of concrete. The pipe sections are preferably provided with the concrete coating before they are welded together on the vessel, and the opposite free end portions of the pipe section are exposed to facilitate the welding operation. The concrete layer should not only fulfill the usual conditions regarding strength and durability, but it could also be necessary to add heavy aggregates, such as iron ore in order to obtain a required high specific weight of the concrete.
Two different methods for providing pipe or tube sections with an outer layer of concrete are known, namely impingement and compression coating. Both of these methods in which the horizontally arranged tube is rotated and moved past a stationary coating machine, involves waste of concrete mixture and insufficient compression of the concrete. The insufficient compression of the concrete necessitates a relatively high content of heavy aggregates to obtain the necessary specific weight. Danish patent specification No. 155.460 discloses a method in which a horizontally extending tube is rotated slowly while concrete is applied to the full length of the tube, and the concrete is being shaped and vibrated by means of a mould surface provided with vibrators. This method has apparently not been used in practice. Danish patent application No. 644/84 discloses a sliding mould which may be used for applying ground-moist concrete to a steel pipe, which is positioned vertically.